JPS6354243B2 - - Google Patents

Description

Detailed Description of the Invention This invention delays the time of an analog electrical signal using an acousto-optic method, and by changing the delay time at high speed, the time axis of the signal can be compressed, expanded,
The present invention relates to an electrical signal time base conversion device that performs reversal and sample and hold operations.

Several methods have been considered for time delaying analog electrical signals. The first method is to temporarily store electrical signals in a digital memory or the like and control the readout time. Devices based on this method are highly versatile and can be expected to have high accuracy, but they require a large number of memory elements to ensure the accuracy of waveform reproduction of analog signals.
and A-D (analog-digital) and D
- Requires an A converter. Therefore, the device has a very complicated structure and is expensive. Then CCD
(Charge Coupled Device), BBD (Bucket
There is a method using a signal transfer delay element such as a Brigade Device, but this method also requires a large number of elements and a complicated electric circuit in order to obtain a good delayed signal waveform. In addition, SAW (Surface Acoustic
The method using a wave (surface acoustic wave) element also requires a complicated circuit configuration as in the above example, and has the drawback that the delay time is determined by the element shape and cannot be easily varied. Furthermore, there are methods of recording analog signals on magnetic tape and controlling the playback time, but these methods that involve mechanical operations have the drawback of increasing the size of the device, or problems with operating time and stability. There is.

As described above, it is very difficult to easily and accurately delay the time of analog signals using electronic circuits or mechanical devices.

The present invention uses an acousto-optic spatial signal processing method for time axis processing of electrical signals, converts analog electrical signals into ultrasound signals, spatially temporarily stores them, and transmits the ultrasound signals at appropriate times for signal detection. This ultrasonic signal is detected using sound waves and light, and the delay time of the detection signal is changed by controlling the detection time and detection position, and the time axis of the electric signal is compressed, expanded, reversed,
It is an object of the present invention to provide a time axis conversion device for electrical signals that performs sample and hold operations.

According to the present invention, an analog electrical signal to be processed is applied to a first ultrasonic transducer placed inside an acousto-optic cell filled with an ultrasonic propagation medium such as a liquid; It is emitted as an ultrasonic signal. This ultrasonic signal retains the information of the analog electrical signal in a spatial form until it reaches and is absorbed by an ultrasonic absorbing member disposed opposite to the ultrasonic transducer surface. At this time, the time axis of the analog electrical signal corresponds to a spatial axis set in the propagation direction of the ultrasonic signal, and the reading of spatially held information is performed by specifying the position coordinates of the spatial axis. This is performed using an ultrasonic beam emitted from the second transducer, and information at the designated position is detected using light. That is, when a narrow ultrasonic beam is emitted to a spatial position to be detected while irradiating plane wave light to the entire ultrasonic signal in the cell based on the analog electric signal, two ultrasonic waves are generated when viewed from the light traveling direction. A specific phase change occurs in the plane wave light that passes through the overlapping part, which is different from that in other parts.
This phase change can be converted into a light amount change with one lens, and the electrical signal obtained by photoelectrically converting this light amount change is proportional to the squared amplitude of the analog electrical signal. Therefore, the electrical signal obtained by photoelectric conversion is the analog electrical signal delayed by using the ultrasonic propagation time, and the delay time is the overlap between the first transducer and the two ultrasonic waves. It is the value obtained by dividing the spatial distance to the matching portion by the ultrasonic propagation speed within the cell. Since the emission position and emission time of the ultrasonic beam are controlled by electrical signals, the delay time can be changed quickly and minutely, and the signal sampling operation is controlled by the presence or absence of the ultrasonic beam. Since it is possible to obtain sampling signals with different delay times of input analog electrical signals. The delay times of these sampling signals are obtained by changing them in a controlled manner little by little, and by converting them into continuous signals using an electric filter circuit, the analog electrical signals are subjected to time axis processing such as temporal expansion and compression. I can get a signal.

Next, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram of an embodiment of an acousto-optic cell for electrical signal processing (hereinafter referred to as an acousto-optic cell in the detailed description of the invention) 1, which is one of the constituent elements of the present invention. The cell is filled with an ultrasonic propagation medium 2 such as a liquid, and has a pair of light transmitting windows 3a on both opposing walls that allow the light beam to pass through.
3b, and a first transducer 4 is arranged so that ultrasonic waves are emitted perpendicular to the traveling direction of the light beam passing through this window. Further, an ultrasonic beam that is perpendicular to the traveling direction of the light beam and spatially intersects with the ultrasonic wave emitted from the first transducer is provided at a location a predetermined distance away from the first transducer. One or more second oscillators 5 are arranged for emitting . Furthermore, as shown in FIG. 2, ultrasonic absorbing members 6a and 6b are provided on the wall facing the first and second transducers to absorb ultrasonic waves and prevent unnecessary reflections. and a signal input terminal 7 for applying a signal to each vibrator individually.
a and 7b are provided.

FIG. 3 shows the relationship between the ultrasound signal 8 and the ultrasound beam 9 inside the acousto-optic cell. Analog input signal 10 shown in figure a
A sine wave signal having a frequency _S whose amplitude is modulated by the oscilloscope is applied to the signal input terminal 7a, and is emitted as an ultrasonic signal 8 into the cell by the first vibrator 4. This ultrasonic signal causes an optical phase grating to be formed within the cell due to a change in the density of the ultrasonic propagating substance. This phase grating is a one-dimensional progressive sinusoidal grating having a grating constant of (v/ _S ), where the speed of sound in the cell is v, and the maximum value of the sinusoidal amplitude is The entanglement line indicating the maximum value of the density change in the range is determined by the analog input signal.

Next, as shown in FIG. 3b, at a position a distance Ld away from the first vibrator 4 in the x direction,
Consider a case where one of the second transducers 5 emits an ultrasonic beam 9 perpendicular to the direction of incidence of the plane wave light and intersects the ultrasonic signal 8. Let y be the traveling direction axis of this ultrasonic beam. Although the x-axis and the y-axis do not necessarily need to be orthogonal at one point in space, the figure shows a state in which the two axes are orthogonal. The ultrasonic beam is connected to the second ultrasonic beam.
is emitted by applying a sine wave signal of a constant frequency _B to the vibrator 5. This ultrasonic beam forms a one-dimensional phase grating that travels in the y-axis direction within the cell, as in the case of the ultrasonic signal 8 described above. In a region where this ultrasound beam and the ultrasound signal spatially intersect, a two-dimensional phase grating having a sinusoidal distribution in both the x and y axes is formed. The plane wave light flux that has passed through this two-dimensional phase grating undergoes a two-dimensional phase change depending on the state of the grating, but by keeping the intensity of the ultrasonic beam constant, the amount of change and the distribution of the change can be controlled by the analog input signal. 1
This is due to a change only in the amplitude value of 0. Therefore, the ultrasonic wave caused by the analog input signal shown in Figure a propagates within the cell as shown in Figure b,
When the ultrasonic beam is emitted so as to cross this, a phase change occurs in the plane wave light that has passed through the two-dimensional phase grating portion, which corresponds to the area value of the shaded area of the analog signal in FIG. If the length P of the ultrasonic beam 9 in the x-axis direction is sufficiently small compared to the minimum spatial period of the analog input signal within the cell, the area value of the diagonal line portion approximates the amplitude value of the analog input signal. Therefore, by detecting the two-dimensional change in the plane wave light flux that caused the phase change using an optical method described later, the analog input signal waveform delayed by the time (Ld/v) can be obtained. Can be done.

Next, consider sampling the analog input signal 10 by emitting the ultrasonic beam 9 for a short period of time. FIG. 4 shows a single ultrasonic beam, that is, a pulsed ultrasonic wave 11, transmitted to one of the second transducers 5.
The figure shows the case of firing from one side to the other. The spatial length of this pulsed ultrasonic wave is made equal to the length W _y of the light transmission windows 3a, 3b in the y-axis direction. In FIG. 1A, in order to make the explanation easier to understand, the ultrasonic signal 8 is fixed, and two ultrasonic waves are shown to overlap due to the movement of the pulsed ultrasonic wave 11. The pulsed ultrasonic wave crosses the ultrasonic signal relatively obliquely from the position indicated by A to the position C. Since the speed of the ultrasonic wave is v, the time T _S for this pulsed ultrasonic wave to cross the light transmission window is T _S =2W _y /v, and the length of the ultrasonic signal in the y-axis direction is W of the window. If it is larger than _y , the value of T _S becomes the time required for one sampling operation. The signal obtained as a result of sampling takes the form of a change in the amount of light as described above, so if it is photoelectrically converted, it becomes a triangular wave with a time period T _S as shown in b of the figure. As shown in the figure,
The value at point B' indicates the output value at point B when the pulsed ultrasonic wave 11 completely overlaps the light transmission windows 3a and 3b in figure a, and the sampling value is displayed. However, during the photoelectric conversion, the amplitude value of the sampling output signal 12 becomes a value proportional to the square of the amplitude value of the analog input terminal 10 due to the square characteristic of the photoelectric converter. Analog input signal 1 in square compressed form
It is compared with 0. Here, the same second vibrator 5
If the pulsed ultrasonic wave is emitted repeatedly with a time period T _S , a triangular repetitive waveform as shown by the dotted line in Figure b is obtained, and the envelope connecting the vertices of these triangular waves is the delayed waveform of the analog input signal. It shows.

Next, consider emitting pulsed ultrasonic waves 11 from a plurality of second transducers 5 in a certain order. The basic firing order is to
Let us consider the case where the oscillators are vibrated one by one in one direction. FIG. 5 shows this situation. In FIG. 1A, the ultrasonic signal is shown as its amplitude value envelope, that is, the analog input signal waveform, and the pulsed ultrasonic wave shows only the movement trajectory from A to E as a solid line. Further, the output value at the point indicated by a black circle is the maximum value of the sampling output signal. The movement trajectory of the broken line is shown in Figure 4 above.
As explained in the figure, a case is shown in which pulsed ultrasonic waves are emitted from a single second transducer. As is clear from the sampling output signals shown in FIG. As a result, a delayed signal in which the time axis of the analog input signal is compressed is obtained. At this time, x of the pulsed ultrasonic wave 11
If the moving speed v _P in the direction is V _P = P'/T _S , the time axis compression ratio k _C of the analog input signal is k _C (v-v _P )/v (1) . In the same equation, when v _P =0, that is, when pulsed ultrasound is emitted from a single second vibrator 5, k _C =1. Further, when the value of v _P is a positive value, that is, the moving direction of the pulsed ultrasound is in the direction away from the first transducer 4, the value of k _C becomes a decimal number, which means time axis extension. Furthermore, in the case of v=v _P , the moving speeds of the ultrasonic signal and the pulsed ultrasonic wave in the x-axis direction are equal, and the value of v _P becomes even larger when k _C =0, which results in a sample hold state. , when the moving speed of the ultrasonic signal exceeds v, the value of k _C becomes negative and a delayed signal with a reversed time axis is obtained. This situation is shown in FIG. Similar to FIG. 5, FIG. 5a shows the trajectory of the analog input signal 10 and the pulsed ultrasonic wave, and FIG. 5b shows the output signal.

According to the above explanation, if the ultrasonic signal existing in the acousto-optic cell 1 is scanned and detected in the ultrasonic propagation direction using a plurality of pulsed ultrasonic waves, the time axis of the ultrasonic signal can be compressed, expanded, It was shown that reversal and sample hold can be achieved. These time axis processes can be realized by the relationship between the sampling period determined by the x-axis movement speed v _P of the pulsed ultrasound 11 and the signal delay time due to ultrasound propagation within the cell, so the above v The maximum frequency of analog input signals that can be processed is limited by the value of _P.

Next, an optical method for detecting the degree of overlapping of two ultrasonic waves within the acousto-optic cell 1 will be described. As shown in FIG. When the light is focused, a two-dimensional diffraction image is generated at the focal plane 14 of the lens. Figure b shows the acousto-optic cell 1 seen from the optical axis direction.
Figure c shows a spatial optical filter 15 whose α and β axes are spatially parallel to the x and y axes of figure b. The spatial optical filter is arranged at the focal plane and detects a desired diffraction image bright spot. Now, since the grating constant of the ultrasonic signal 8 in the cell is v/ _S , the diffraction image by this sine wave grating is generated on the α axis on the filter surface by the Fraunhofer diffraction principle. It occurs at a point that is ±d _S away from the axis point. The value of d _S is expressed as d _S = ±(λF _S )/v (2), where λ is the wavelength of the plane wave light, and F is the length of the lens 1.
It has a focal length of 3. Similarly, the diffraction image bright spot due to the pulsed ultrasound is generated at a location on the β axis, away from the optical axis by ±d _B. The value of d _B is expressed as d _B =±(λF _B )/v (3) where _B is the sine wave (carrier wave) frequency of the pulsed ultrasound. In the present invention, the diffraction image to be detected is
Since it is limited to only the bright spot of the next diffraction, the above equations (2) and (3)
The values of d _S and d _B indicate the position of the first-order diffracted light. A diffraction bright spot due to plane wave light passing through a region where the two ultrasonic waves overlap is formed by the plane wave light diffracted in the α-axis direction by the ultrasonic signal and further diffracted in the β-axis direction by the pulsed ultrasonic wave. what you did,
Alternatively, it can be considered to be the opposite, and occurs at the positions R 1 to R ₄ (±d _S , ±d _B ) on the filter surface.
FIG. 7c shows the positions of these bright spots. As described above, by detecting one or more of these four bright spots while keeping the amplitude value of the pulsed ultrasound constant, a delayed sampling output signal of the analog input signal can be obtained.

FIG. 8 is an overall configuration diagram of an embodiment of the electric signal time axis conversion device of the present invention. Signal input terminal 1
6, the square root calculation circuit 17 performs square compression of the amplitude. The purpose of this square compression is to correct the square characteristic of the photoelectric converter 18 in photoelectric conversion during delayed signal detection, and to provide a proportional relationship to the input/output signal amplitude of this device. Of course, this circuit is not required if the analog input signal is a binary signal. Now, the output signal of the square root calculation circuit 17 is sent to the first amplitude modulation circuit 19.
A sinusoidal carrier wave generated by an oscillator 20 is amplitude-modulated. This amplitude-modulated sinusoidal signal is applied to a first transducer 4 installed inside the acousto-optic cell 1, and is emitted as an ultrasonic signal 8 into the ultrasonic propagation material 2 within the cell. be done. On the other hand, the second sine wave carrier generated by the second oscillator 21 is sent to a distribution circuit 22 having a plurality of output terminals, and the plurality of outputs are output according to a sweep control signal sent from a sweep control circuit 23. It is distributed sequentially and regulatedly to the terminals. The plurality of output terminals are connected to a plurality of second transducers 5 arranged in the cell in a certain order, whereby a pulsed ultrasonic beam is transmitted from the second transducer. are fired sequentially as if scanning the inside of the cell. In the cell, the ultrasonic signal 8 scanned by the ultrasonic beam modulates the phase of the plane wave light passing through the light transmission windows 3a and 3b of the cell, and receives this phase modulation. Lens 13 for plane wave light
is focused to produce a diffraction image. Of this diffraction image,
If only the bright spots generated by the overlap of the ultrasound beam and the ultrasound signal are detected by the spatial optical filter 15 and converted into electrical signals by the photoelectric converter 18, the delay of the analog input signal can be reduced. Sampled output signals at different times are obtained. This output signal is passed through an electrically reduced pass filter 2.
4 and detecting the envelope waveform, as already explained in detail, a signal obtained by time-base compression, expansion, inversion, and sample-holding of the analog input signal can be obtained.

The present invention has the above configuration, and includes the first and second
transducers 4, 5 and ultrasonic absorption members 6a, 6b
Plane wave light is incident on an acousto-optic cell 1 having an inner wall thereof, and an ultrasonic signal is emitted from the transducer into an ultrasonic propagation substance 2 filled in the cell to generate the plane wave light. This phase change is applied to the lens 13 and the spatial optical filter 1.
The envelope waveform of the electric signal applied to the first vibrator, that is, the analog input signal, can be obtained with a time delay by detecting the signal using an optical method using the oscillator 5 and photoelectrically converting the signal. Furthermore, the sweep control circuit 2 controls the emission time and emission position of the ultrasonic beam for signal detection emitted from the second transducer.
3, it is possible to obtain sampling output signals with slightly different delay times of the analog input signal, so this signal is demodulated with a low-pass filter and the delay time of the analog input signal is determined in a regular order. It has the effect of being able to obtain signals whose axes have been transformed, that is, signals of time axis compression, expansion, inversion, and sample hold.

In the present invention, it is not necessarily necessary to superimpose two ultrasonic signals inside the acousto-optic cell 1, but it is sufficient that the two ultrasonic waves overlap each other when viewed from the optical axis direction. Therefore, if necessary, it is possible to easily adjust the optical system by using a multi-cell structure using dedicated cells for each of the ultrasound signals and ultrasound beams, or by using different materials for the ultrasound propagation medium. It is also possible to improve the ultrasonic beam to pass through the ultrasonic signal quickly and shorten the sampling period.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the structure of an acousto-optic cell for electrical signal processing, Figure 2 is a diagram showing the arrangement of a transducer and an ultrasonic absorption member in the acousto-optic cell, and Figure 3 is a diagram showing the arrangement of an acousto-optic cell. Figure 4 is a diagram showing the state of sampling by pulsed ultrasound, Figure 5 is a diagram showing an example of time axis compression processing, and Figure 6 is an example of time axis reversal processing. FIG. 7 is a diagram showing an optical detection method of the output signal,
FIG. 8 is a diagram showing the configuration of an embodiment of the present invention. 1 is an acousto-optic cell for electrical signal processing, 2 is an ultrasound propagation medium, 3a and 3b are light transmission windows, 4 is a first transducer, 5 is a second transducer, and 6a and 6b are ultrasound absorbing members. , 13 is a lens, 15 is a spatial optical filter, 17 is a square root calculation circuit, 18 is a photoelectric converter, 19 is an amplitude modulation circuit, 22 is a distribution circuit, 23
indicates the sweep control circuit.

Claims (1)

[Claims] 1. A square root calculation circuit 17 for signal input; An amplitude modulation circuit 19 that amplitude-modulates a first sine wave signal using the circuit output to produce a first electric signal; and distributes a second sine wave signal to a plurality of terminals. a distribution circuit 22;
a sweep control circuit 23 that controls the signal distribution operation of the distribution circuit; an acousto-optic cell for electrical signal processing filled with an ultrasonic propagation medium, which is provided on both opposing walls of the cell and that allows light to pass through; Transparent window 3
a, 3b, a first oscillator 4 that converts the first electric signal into a first ultrasonic wave and radiates it into the medium perpendicular to the light traveling direction of the light beam, and from the first oscillator. The second sine wave signal is arranged at a predetermined distance in the ultrasonic radiation direction and connected to a plurality of output terminals of the distribution circuit, and converts the second sine wave signal into a second ultrasonic wave, and is arranged perpendicularly to the light traveling direction and connected to a plurality of output terminals of the distribution circuit. a plurality of second oscillators 5 that radiate into the medium so as to intersect with the first ultrasonic waves; and the first and second vibrations for absorbing the first and second ultrasonic waves. Ultrasonic absorption members 6a and 6b provided opposite to each other
an acousto-optic cell 1 for electrical signal processing;
A lens 13 that focuses the light beam transmitted through the cell.
and; a spatial optical filter 15 that detects a bright spot at a predetermined position in the diffraction image created by the lens;
a photoelectric converter 18 that converts the optical output of the filter into an electrical signal, and the predetermined position of the bright spot is set at a frequency of the first and second sinusoidal signals and the first and second superpositions with respect to the optical axis. determined in relation to the radiation direction of the sound wave, and the brightness of the bright spot is determined in relation to the amplitude values of the first and second ultrasound waves at the intersection position,
The output signal of the photoelectric converter is delayed by a time determined in relation to the predetermined distance at which the desired second transducer is disposed and the propagation speed of the first ultrasonic wave. An electrical signal time axis conversion device characterized by: